The 3GPP has been making a study on specification of a home base station (second radio base station) Home Node B used in a mobile communication system employing the UTRAN (Universal Terrestrial Radio Access Network) system.
FIG. 5 shows a configuration of the UTRAN mobile communication system. As shown in FIG. 5, the UTRAN mobile communication system includes a core network apparatus CN, a radio controller RNC, a macro radio base station (first radio base station) Node B and a home radio base station (second radio base station) Home Node B.
Here, the macro radio base station Node B is a normal radio base station installed by a communication carrier or the like, whereas the home radio base station Home Node B is a small radio base station installed inside a house or the like by a general user, a communication carrier or the like (also called a femto radio base station).
Note that the UTRAN mobile communication system is configured so that a user signal is transmitted and received via a U-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the radio controller RNC, and via a U-plane interface between the radio controller RNC and the core network apparatus CN.
On the other hand, a control signal is configured to be transmitted and received via a C-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the radio controller RNC, and a C-plane interface between the radio controller RNC and the core network apparatus CN in the UTRAN mobile communication system.
In addition, FIGS. 6 and 7 respectively show two types of configurations of the UTRAN mobile communication systems employing the HSPA (High Speed Packet Access).
As shown in FIG. 6, such a UTRAN mobile communication system of the first type includes a core network apparatus CN, a radio controller RNC, a macro radio base station (first radio base station) Node B and a Home Node B (second radio base station).
In addition, as shown in FIG. 7, such a UTRAN mobile communication system of the second type includes a core network apparatus CN, a macro radio base station (first radio base station) Node B and a home radio base station (second radio base station) Home Node B.
Specifically, the aforementioned UTRAN mobile communication system of the first type is configured to cause a part (U-plane function) of the functions of the radio controller RNC to transition to the macro radio base station Node B and the home radio base station Home Node B.
Moreover, the aforementioned UTRAN mobile communication system of the second type is configured to cause all of the functions of the radio controller RNC to transition to the macro radio base station Node B and the home radio base station Home Node B.
Note that, in the aforementioned UTRAN mobile communication system of the first type, a user signal is configured to be transmitted and received via a U-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the core network apparatus CN, whereas a control signal is configured to be transmitted and received via a C-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the radio controller RNC, and a C-plane interface between the radio controller RNC and the core network apparatus CN.
Moreover, in the aforementioned UTRAN mobile communication system of the second type, a user signal is configured to be transmitted and received via a U-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the core network apparatus CN, whereas a control signal is configured to be transmitted and received via a C-plane interface between the macro radio base station Node B or the home radio base station Home Node B and the core network apparatus CN.
FIG. 8 shows a protocol stack according to the C-plane interface between the radio base station Home Node B/Node B and the higher-level node (radio controller RNC or core network apparatus CN).
As shown in FIG. 8, a TNL (Transport Network Layer) and an RNL (Radio Network Layer) are defined as the protocols used in the aforementioned C-plane interface.
Here, in the UTRAN mobile communication system, an SCTP (Stream Control Transmission Protocol) connection (control signal connection) is configured to be established by a request from a higher-level node (radio controller RNC, for example).
As shown in FIG. 9, the higher-level node is configured to transmit an SCTP “INIT (control signal connection establishment request)” to the home radio base station Home Node B or the macro radio base station Node B, when detecting that no SCTP connection (control signal connection) is established with the home radio base station Home Node B or the macro radio base station Node B.
The home radio base station Home Node B, however, is a small radio base station installed inside a house or the like. A general user can install a home radio base station Home Node B by himself or herself. In addition, the user can freely turn on or off the power of the home radio base station Home Node B.
Accordingly, there arises a problem in a case where the home radio base station Home Node B is installed by a general user and where the power of the home radio base station Home Node B is turned off by the user. In this case, the higher-level node has to repeatedly transmit the SCTP “INIT (control signal connection establishment request)” although such transmission is useless, thereby causing an increase in the processing load.